1. Field of the Invention
The present invention relates to a semiconductor manufacturing apparatus, and more particularly to a bias sputtering apparatus for depositing an insulating thin film on a substrate.
2. Discussion of Background
Presently, a sputtering method is widely employed for formation of wiring materials and insulating thin films for use in integrated circuits. Such a sputtering method makes a thin film by introducing Ar gas into a vacuum vessel and applying direct current or radiofrequency power to a cathode including a target material mounted thereon to cause glow discharge. As a result of this glow discharge, a target surface is negatively biased (called a self bias) with respect to the plasma, and Ar ions accelerated by this bias voltage collide with the target surface to subject the target material to sputtering and etching. Material particles so etched are deposited on a wafer located in opposition to the target for film making. In contrast, there is known the so called radiofrequency bias sputtering process wherein radiofrequency power is applied to a succeptor itself including the wafer mounted thereon as well as the target to deposit a film on the wafer surface, while sputtering and etching are effected by the self bias formed on the wafer surface simultaneously with the film deposition on the wafer surface.
FIG. 5 is a schematic cross-sectional view of a typical conventional bias sputtering apparatus. Designated at 501 is a target composed of a material such as SiO.sub.2, Si.sub.3 N.sub.4, Al.sub.2 O.sub.3, AlN and the like for example, and 502 designates a target electrode including the target mounted thereon. Moreover, designated at 503 and 504 are respectively a semiconductor wafer and a succeptor electrode. Radiofrequency power is supplied to the target electrode 502 and the succeptor electrode 504 via a matching circuit, and a vacuum vessel 505 is grounded. For this application, a radiofrequency (RF) power source having an oscillation frequency of 13.56 MHz is typically employed. Moreover, for an actual apparatus, besides those members described above, a vacuum exhaust unit, a gas introduction inlet, and a mechanism for taking the wafer into and out of the apparatus are provided, but are not shown in the figure for the sake of brevity.
The surfaces of the semiconductor wafer 503 and the succeptor 504 are negatively biased with respect to the plasma by the RF power applied to the succeptor, with which the Ar ions accelerated by an electric field caused by the self bias collide to permit the deposited film to be partly resputtered. Such a radiofrequency bias sputtering method assures a thin film excellent in mechanical strength. In addition, this radiofrequency bias sputtering method also enables a flat surface film to be formed by making use of a property of the film, that film formed at a stepped portion is likely to be sputtered. This method however suffers from a severe problem during manufacturing a semiconductor integrated circuit in that the substrate of the semiconductor wafer is damaged due to the collision of the Ar ions accelerated by the self bias with the semiconductor wafer resulting in deteriorated characteristics of the constituent elements. These problems hinder the bias sputtering apparatus from being put into practical use.